1. Field of the Invention
The present invention relates to a process for isomerizing a compound having an acyloxyl group or a hydroxyl group at the allylic position thereof. The present invention also relates to a process for isomerizing 3,4-disubstituted-1-butene and/or 1,4-disubstituted-2-butene using a specific catalyst to produce, respectively, the corresponding isomers, 1,4-disubstituted-2-butene and/or 3,4-disubstituted-1-butene.
2. Discussion of the Background
1,4-diacetoxy-2-butene is an important intermediate for producing 1,4-butanediol, tetrahydrofuran or the like. 3,4-diacetoxy-1-butene is an important intermediate for producing medicines, agricultural chemicals, various aromatics, terpentene compounds such as vitamin A acetate, and the like.
It is known that 1,4-diacetoxy-2-butene and 3,4-diacetoxy-1-butene may be obtained by oxidizing butadiene in an acetic acid solvent with molecular oxygen (e.g., Laid-Open Japanese Patent Application (JP-A) Nos. 48-72090, 48-96513). However, it is extremely difficult to produce 1,4-diacetoxy-2-butene and 3,4-diacetoxy-1-butene in an arbitrary ratio by this method, since the production ratio of 1,4-diacetoxy-2-butene to 3,4-diacetoxy-1-butene is influenced mainly by the ability of the catalyst.
Although 3,4-diacetoxy-1-butene is easily obtained by acetoxylating 1,2-epoxy-3-butene, it is extremely difficult to obtain 1,4-diacetoxy-2-butene by this method. On the other hand, extremely specific raw materials such as 3,6-dihydro-1,2-dioxine and the like are required for producing only 1,4-diacetoxy-2-butene selectively. Therefore, it is virtually impossible to produce 1,4-diacetoxy-2-butene on an industrial scale.
Accordingly, conventional methods for isomerizing 3,4-disubstituted-1-butene and/or 1,4-disubstituted-2-butene using a particular catalyst have been suggested to produce the corresponding respective isomers, 1,4-diacetoxy-2-butene and/or 3,4-diacetoxy-1-butene. These include, for example, a method using a platinum chloride compound as a catalyst (DE U.S. Pat. Nos. 2,736,695 and 2,134,115), a method using a palladium compound in combination with hydrogen chloride or hydrogen bromide (JP-A No. 57-140744), a method using a PdCl.sub.2 (PhCN).sub.2 compound (U.S. Pat. No. 4,095,030) and the like. However, these methods use a halogen compound as a catalyst and have problems with the stability of the catalyst. These methods are undesirable industrially since they require large amounts of corrosive halogen compound.
Methods are known which avoid the use of halogen compounds, and these include a method using a catalyst composed of a palladium compound and an organic phosphine (JP-A No. 55-11555) and a method of conducting isomerization in a gas phase using an acid catalyst such as alumina, zeolite and the like (DE-Patent No. 3326668, JP-A No. 50-126611). However, these methods have problems in that either the activity of the catalyst is unsatisfactory or the selectivity of the catalyst is not sufficient and the like, and, accordingly, these methods are unsatisfactory from an industrial point of view.
As described above, 1,4-diacetoxy-2-butene and 3,4-diacetoxy-1-butene are intermediates for utterly different product groups, as noted above. Since each intermediate is useful in widely varying applications, the desired ratio, e.g., in a mixture of 1,4-diacetoxy-2-butene and 3,4-diacetoxy-1-butene depends greatly on area, era or business background of an enterprise carrying them out. Namely, it is extremely significant to isomerize 3,4-diacetoxy-1-butene and/or 1,4-diacetoxy-2-butene to produce the corresponding respective isomers, ,4-diacetoxy-2-butene and/or 3,4-diacetoxy-1-butene, according to industrial needs.